The attorney general agreed to submit a request for a new investigation into the asthma death of a nine-year-old girl.
He acted after hearing new evidence linking Ella Kissi-Debrah's death to illegal levels of air pollution near her home in South London.
The lawyers who acted for the family said it was an "extremely important" step.
No individual death was previously officially linked to illegal levels of air pollution.
In August, Ella's mother, Rosamund Adoo-Kissi-Debrah, handed a 1
He said, "I have concluded that there is new evidence that can alter the substantive truth of Ella's death.
" I am therefore able to give my permission for a request to the High Court to request a new one. investigation, based on the evidential test being achieved. "
" The Right Decision "
She lived in Lewisham, south of London, 25 m (80 feet) from the South Circular Road – a known" hotspot "of pollution.
She died in February 2013 after having lived three years of convulsions
During this period, levels of local air pollution regularly breach the legal limits of the EU, its last fatal attack occurred during a peak of atmospheric pollution levels.
2014 found she has D died of acute respiratory failure and severe asthma.
However, the decision of the attorney general paved the way for a new investigation to determine whether "illegal levels of air pollution" were partially the cause of his death.
Ms. Adoo-Kissi-Debrah said: "It's great, it's the right decision and now we can get to the bottom of the impact on the health of air pollution on young people.
"We hope that if we succeed, national government, local government and individuals must do something to clean up the air It is unacceptable that today children in Britain die from asthma."
Human rights lawyer Jocelyn Cockburn of Hodge Jones and Allen is acting on behalf of the family.
Described the decision as "extremely strong" and said that the implications went well beyond the case of Ella.
"A more extensive investigation concerned not only what happened to Ella and the circumstances of her death, but what steps were taken and what lessons could be learned.Watch the broader implications for the health of children in that area, "Mrs. Cockburn said.
"For me, this case gives an opportunity for those people in a public office to protect our health, to be asking questions and being accountable and finding solutions so we can proceed to clean up the 39, air as quickly as possible. "
" Striking association "
One reason to call a new investigation was that permitting illegal levels of air pollution was a potential violation of human rights under Article 2 of the European Convention on Human Rights – which protects the right to life.
Ms Cockburn said: "A new investigation could mean that a wide range of" stakeholders "could be called to testify. This could include the local authority, the mayor of London along with the NHS Trust and Defra premises. . "
The decision of the attorney general followed a report by prof. Stephen Holgate, a leading expert on asthma and air pollution, has found a "surprising association" between Ella's hospital admissions and recorded peaks of nitrogen dioxide (NO2) and PM10, the most harmful pollutants.
His report said that there was a "real prospect that without illegal levels of air pollution, she would not have died".
She often went to school along the South Circular Road and Lewisham High Street, a journey that took between 30 and 40 minutes. Or she would have been forced to sit for long periods in traffic jams
. She was taken to hospital for the first time in 2010 after a cough attack that followed a peak in air pollution levels.
No connection explained
was subsequently hospitalized 27 times over a period of three years. Many of these coincided with peaks recorded in atmospheric pollution.
His mother said that he had revived Ella between 20 and 30 times while waiting for an ambulance.
She had been treated in five separate hospitals but without doctors had ever explained that air pollution could worsen asthma.
The next legal step is that the application be brought to the High Court, which will decide whether it is "desirable or necessary" to have a new investigation.
While the High Court has the last word, it is very unusual that the court does not agree with the attorney general. According to Mrs. Cockburn, the decisions made by the attorney general are "indisputably indisputable".